The present invention relates to new stabilized compositions based on halogenated polymers and more specifically on chlorinated polymers. Halogenated polymers tend to dehydrohalogenate to release hydrohalogenic acid when being processed with heat; this results in the formation of polyene double bonds which are responsible for coloring the polymers.
Chlorinated polymers, for example, especially polyvinyl chloride (PVC), dehydrochlorinate to release hydrochloric acid when processed with heat. Numerous additives have been recommended to deal with this problem, on the one hand to limit the formation of hydrochloric acid or to fix it and on the other hand to decelerate the propagation of polyene double bonds. Reference may be made, for example, to The Stabilization of Polyvinyl Chlorides by F. Chevassus (Amphora Publications, 1957).
Among the compounds useful as additives which have been known for a long time, and are still very widely employed, are lead compounds and organostannic compounds.
Because of their toxicity, the use of lead compounds is restricted to the nonalimentary applications of chlorinated polymers, such as formulations for various types of pipes, parts for the building industry or formulations for the protection of electrical cables. Organostannic compounds are employed in the majority of applications of chlorinated polymers, whether alimentary or nonalimentary.
An acceptable stabilization of chlorinated polymers, and more particularly of PVC, in most cases requires the joint use of a number of stabilizers which act in a complementary and sometimes synergistic manner.